A testing and measuring device of the kind first mentioned above is described in U.S. Pat. No. 4,420,567.
The reliable detection of hydride gases such as arsine or phosphine as highly toxic constituents in chemical processes, such as in the semiconductor industry, is becoming ever more necessary and requires an apparatus which can be manipulated in a simple manner and which provides a reliable indication. The known indicator operates on the principle of coloration change of an indicator substance in the presence of the hydride gas to be detected. An indicator is impregnated, for example, on a paper tape and provided with impregnation additives. The degree of coloration is measured either by a color comparison or by a linear coloration of the indicator tape. Spectro-photometric evaluation possibilities are also available.
The constituents of the known indicator include silver nitrate together with an acid and a glycol impregnated on a carrier substrate. Since the silver nitrate alone is light sensitive and a long-term stability of the indicator is assured only in short time spans, an acid additive is required to improve the long-term stability. However, this indicator provided with an acid additive also shows an unchanged detection characteristic only over a time span of approximately six months. This stabilization duration is too short to prevent a light-induced coloration of the indicator over a longer time span. However, this is desirable since the storage capability of the unused indicator is required over a significantly longer time span. Faulty measurements because of the effect of light during the detection of the hydride gas have to be avoided.
A further indicator for hydride gases is described in European Patent Publication EP-Al 206 815. A copper salt is used as a detecting reagent and especially copper carbonate is utilized. This detection system is however not sufficiently recognizable with respect to hydride gases in its coloration because the initial blue color of the indicator in the presence of the hydride gas turns black; however, this color change cannot be detected with the naked eye especially for small concentrations to be detected. Accordingly, this known indicator is only suitable where high concentrations are to be detected.